Rail Breakages
There are many reasons why rails break. In jointed track, metallurgical failure at the joint is often experienced; bolt holes at fishplates generate high shear stresses in the rail web material, in extreme cases leading to star cracks at the bolt hole.
Wheelburns occur when high temperatures are generated if a driven axle rotates with no, or little, forward movement; this changes the metallurgy of a rail, causing embrittlement. Other metallurgical changes take place due to the phenomenon of gauge corner cracking (in which fatigue microcracking propagates faster than ordinary wear) and also due to the effects of hydrogen inclusion during the manufacturing process, leading to crack propagation under fatigue loading.
Read more about this topic: Derailment
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